1. Field of the Invention
The present invention relates to a disk controlling method and a disk controlling apparatus and, more particularly, to a disk controlling apparatus in which a data recording region is divided in a radial direction into a plurality of zones, the recording frequency is increased in conformity to the distance of a zone from the center of the data recording region so as to make the data recording density uniform in each zone, thereby an outer zone is provided with a larger track capacity than an inner zone, and to a disk controlling method for the disk controlling apparatus.
2. Description of the Related Art
A magnetic disk subsystem is provided with a magnetic disk apparatus (DASD: Direct Access Storage Device) as an I/O device, and a disk controlling apparatus provided between a host apparatus as a higher-order apparatus and the magnetic disk apparatus so as to control the operation of writing/reading data to/from the magnetic disk apparatus.
FIG. 19 shows the structure of an I/O subsystem (magnetic disk subsystem) composed of modules for respective functions. In FIG. 19, the reference numeral 1 represents a host apparatus (CPU), 2a, 2b channel devices, 3 an I/O subsystem (magnetic disk controlling apparatus ), and 4a to 4d magnetic disk apparatuses as I/O devices. In the I/O subsystem, the reference numerals 5a, 5b represent a plurality of host interface devices (channel adapters) each serving as an interface between the I/O subsystem and a host apparatus, 6a, 6b a plurality of subordinate interface devices (device adapters) each serving as an interface between the I/O subsystem and the I/O devices 4a to 4d, 7 a resource manager for controlling the resource management as a whole and the entire processing operations, 8 a table storage portion for storing various tables which are necessary for the management of the resources, and 9 an internal bus for connecting the channel adapters 5a, 5b, the device adapters 6a, 6b and the resource manager 7 so as to enable the transmission and the reception of data between each other.
Data are written on each track of the magnetic disk apparatus in accordance with a CKD format. FIG. 20 is an explanatory view of the CKD format. Each track has areas divided by gaps, and an index mark is attached to the head of the track. The symbol HA represents a home address area subsequent to the index mark, and the address of the track is written therein. A plurality of records R0, R1, R2 . . . each of which is composed of a count area C, a key area K and a data area D are written in the area subsequent to the home address region HA. In the counter area C, a track address CCHH (CC: cylinder address, HH: head number), a record number R and the lengths K.sub.L, D.sub.L of the subsequent key area and data area), etc. are written. Accordingly, by designating the track address and the record number, it is possible to designate each record. Although a key for retrieval is written in the key area K, this is not essential. User data are written in the data area D.
In the I/O subsystem having the above-described structure, data are written and read out in the following manner. In the following explanation, the I/O subsystem is assumed to be a magnetic disk controlling apparatus DCU. FIG. 21 is an explanatory view of a sequence for a data writing operation.
When a seek command SK is produced by the channel devices (CH) 2a and 2b, the magnetic disk controlling apparatus (DCU) 3 queues the command in a command queue without permitting the magnetic disk apparatuses 4a to 4d to execute a seeking operation. Thereafter, an operation end signal is supplied to the channel devices CH as if the seek operation were finished. Since a positioning time and a rotation waiting time are necessary in a magnetic disk apparatus, a plurality of positioning commands such as a seek command and a set sector command are queued up and the commands in the queue are consecutively executed when a search ID command is received, thereby increasing the processing speed.
When the channel device CH receives the seek operation end signal, it issues a set sector command SS. The magnetic disk controlling apparatus DCU queues the set sector command, and an operation end signal is supplied to the channel devices CH as if the set sector operation were finished.
When the channel device CH receives the set sector operation end signal, it issues a search ID command SID. The magnetic disk controlling apparatus DCU controls a magnetic disk apparatus DASD so as to consecutively execute seek and set sector operations and issues a retry signal so as to separate the channel device CH from the magnetic disk controlling apparatus DCU during the operation. In this manner, the channel device CH is temporarily separated from the magnetic disk controlling apparatus DCU, so that the channel device CH can execute another service or the like to another magnetic disk controlling apparatus. When the channel device CH receives a command request signal from the magnetic disk controlling apparatus DCU after the channel device CH is separated in accordance with the retry signal, the channel device CH supplies again the latest command that it has issued.
When the seek and set sector operations are finished, the magnetic disk apparatus DASD supplies an operation end signal, and in accordance with the operation end signal, the magnetic disk controlling apparatus DCU supplies a command request signal to the channel device CH. When the channel device CH receives the command request signal, the channel device CH reissues the latest command, i.e., the search ID command SID, that it has issued. When the magnetic disk controlling apparatus DCU receives the search ID command SID, the magnetic disk controlling apparatus DCU so controls the magnetic disk apparatus DASD as to execute the search ID operation, and when the search ID operation is finished, the magnetic disk apparatus DASD supplies an operation end signal to the channel device CH.
The channel device CH which has received the command request signal, it issues a write command WD. In accordance with the write command WD, the magnetic disk controlling apparatus DCU so controls the magnetic disk apparatus DASD as to execute the data write operation, and supplies a retry signal to the channel device CH so as to separate the channel device CH from the magnetic disk controlling apparatus DCU during the data writing operation. In this manner, the channel device CH is temporarily separated from the magnetic disk controlling apparatus DCU.
When the data write operation is finished, the magnetic disk apparatus DASD supplies a data write operation end signal to the magnetic disk controlling apparatus DCU, and in accordance with the operation end signal, the magnetic disk controlling apparatus DCU supplies a command request signal to the channel device CH. When the channel device CH receives the command request signal, the channel device CH reissues the latest command, i.e., the write command WD, that it has issued. When the magnetic disk controlling apparatus DCU receives the write command WD, the magnetic disk controlling apparatus DCU immediately transfers the write operation end signal to the channel device CH, thereby completing a series of writing operations.
The internal operations in the magnetic disk controlling apparatus in the above-described data writing operations are, for example, as follows. When a seek command SK is produced by the channel device 2a, the channel adapter 5a queues the command in a command queue and thereafter returns an operation end signal to the channel devices 2a as if the seek operation were finished. When the channel device 2a receives the seek operation end signal, it issues a set sector command SS. When the channel adapter 5a receives the set sector command SS, it queues the command in a command queue and thereafter returns an operation end signal to the channel devices 2a as if the set sector operation were finished. When the channel device 2a receives the set sector operation end signal, it issues a search ID command SID. The channel adapter 5a which has received this command informs the resource manager 7 of the reception of the command, and issues a retry signal so as to separate the channel device 2a from the magnetic disk controlling apparatus 3. The resource manager 7 confirms that the magnetic disk apparatus 4a as an object (which is designated by a start I/O command) is not being accessed by referring to an exclusive control table stored in the table storage portion 8, determines a predetermined device adapter 6a and supplies the identification data for the device adapter 6a to the channel adapter 5a. The resource manager 7 supplies the identification data for the channel adapter 5a to the device adapter 6a. The resource manger 7 also writes in the exclusive control table that the magnetic disk apparatus 4a is being accessed.
The channel adapter 5a supplies the CKD track position (CCHH) contained in the seek command to the designated device adapter 6a and requests it to execute seek operation. When the device adapter 6a receives the request of the seek operation, it instructs the magnetic disk apparatus 4a to execute a seek operation. When the device adapter 6a receives a positioning end signal from the magnetic disk apparatus 4a after completion of the seek operation, the device adapter 6a reports the reception of the positioning end signal to the channel adapter 5a. The channel adapter 5a then supplies the sector value which is contained in the set sector command to the device adapter 6a and requests the device adapter 6 to execute a set sector operation.
Similar processing is executed between the channel adapter 5a and the device adapter 6a, and when the reading/writing operation to the magnetic disk apparatus 5a is finally finished, the channel adapter 5a reports the end of access to the resource manager 7. When the resource manager 7 receives the report of the end of access, it writes in the exclusive control table that the magnetic disk apparatus as the object is not being accessed.
FIG. 22 is an explanatory view of a sequence for a data reading operation. It is the same as FIG. 22 except that a read command RD takes the place of a write command WD.
In a small-size magnetic disk apparatus, the number of revolutions is increased and the amount of floating in the head is reduced for the purpose of high-density recording. However, with a reduction in disk size, the difference in the length between an inner track and an outer track is enlarged. Especially, when the innermost track is brought closer to the center of the disk in order to increase the recording density per disk, the outermost track becomes more than twice as long as the innermost track. As a result, in an outer periphery, the linear speed is high and the bit linear density (recording density) is low, and the closer to the center of the disk, the lower the linear speed and the higher the bit linear density. In other words, the recording density in an inner track is greatly different from that in an outermost track.
To prevent this, a constant density recording (CDR) system is proposed. In this CDR system, a data recording region of a disk DK is divided in a radial direction into a plurality of zones (three zones A, B and C in FIG. 23), as shown in FIG. 23, and the recording frequency is increased in conformity to the distance of a zone from the center of the disk DK so as to make the data recording density nearly uniform in each zone. According to this system, it is possible to limit the recording density in each zone to a predetermined range, and high-density recording is possible all over the disk surface.
In the CDR system, however, the capacity per track (bytes/track) (hereinafter referred to as "track capacity") is different between zones, as shown in FIG. 24. For example, if the capacity (bytes/track) of the zones A, B and C are assumed to a, b and c, respectively, the track capacity in the zone A is 1.5 times of the track capacity in the zone B, and the track capacity in the zone C is 1/2 of the track capacity in the zone B. In a variable-length recording system adopting a conventional CKD format, the software of a host apparatus is produced on the assumption that the track capacity is uniform. For this reason, it is impossible to apply conventional software resources to a disk of a CDR system having different track capacities, which necessitates the trouble of newly producing software from the beginning.
In order to forcibly apply a conventional variable-length recording method to a CDR disk, the disk must be used on the assumption that it has the track capacity of the innermost track. Thus, the efficiency of the disk is greatly lowered, which makes the CDR system adopted for high-density recording meaningless.